1. Technical Field
The present invention relates to a light emitting element/device which is operated by a direct voltage applied thereto.
2. Background Art
Attention has been focused on nitride semiconductors, as practical semiconductor materials for use in light emitting devices, particularly blue-LEDs; blue light emitting diodes and UV-LEDs; Ultra-violet light emitting diodes, among light emitting devices which are operated by application of direct currents thereto. Particularly, attention has been focused on GaN based semiconductors which are represented by gallium nitride (GaN), indium gallium nitride (InGaN) mixed crystals, aluminum gallium nitride (AlGaN) mixed crystals, indium aluminum gallium nitride (InAlGaN) mixed crystals. Researches and developments have been actively conducted regarding these GaN-based semiconductors.
Conventionally, such GaN-based semiconductors have been fabricated as single-crystal thin films by growing the semiconductors on substrates according to MOCVD (Metal Organic Chemical Vapor Deposition) processing. However, it has been extremely difficult to form single-crystal thin films made of GaN-based semiconductors, through MOCVD processing.
On the other hand, as another candidate for light emitting devices which are operated by direct currents, there are organic ELs. Organic ELs have the advantages that they can be fabricated with lower cost, since inexpensive processing such as vapor deposition processing can be employed and, also, inexpensive substrates such as glasses can be employed. However, such organic ELs have the problem of poor reliability.
Therefore, there have been suggested methods which treat inorganic light emitting members as particles rather than as thin films and, further, arranges such phosphor particles for forming a light emitting device. As advantages of the method, regarding inorganic thin-film type light emitting devices, it is possible to form inorganic light emitting members without causing the members to be influenced by substrates and the like, which can improve the crystallinity of the inorganic light emitting members, thereby easily providing larger areas thereof. Further, regarding organic ELs, it is possible to employ inorganic materials rather than organic materials as light emitting members, which offers the advantage of improvement of the reliability.
As an example of a light emitting device including an arrangement of inorganic phosphor particles, there has been disclosed a technique for providing a nitride semiconductor which forms nucleuses and further providing, on the surface thereof, a phosphor layer made of another nitride semiconductor and, further, laminating a nitride semiconductor layer on this phosphor layer, such that the nitride-semiconductor/phosphor-layer/nitride-semiconductor-layer constitute a quantum well structure, as described in Japanese Patent Laid-open Publication No. 2006-117735.